An IGBT (Insulated Gate Bipolar Transistor) is one example of a power semiconductor device. In an IGBT, a p-type collector layer and an n-type base layer are stacked in this order on a collector electrode; and multiple trench gate electrodes are provided thereon with stripe configurations. Then, a p-type base layer is provided in the region between the trench gate electrodes; and an n-type emitter layer connected to an emitter electrode is provided in a portion of the upper layer portion of the p-type base layer.
In the IGBT, a MOS channel is formed in the p-type base layer by a positive potential being applied to the trench gate electrode; electrons are introduced from the n-type emitter layer while holes are introduced from the p-type collector layer; and a current flows between the collector electrode and the emitter electrode.
Recently, a method has been discussed to suppress the emission of accumulated carriers (e.g., holes) proximal to the element surface to reduce the saturation voltage (Vce (sat)) between the collector electrode and the emitter electrode in the on-state. In such an example, an n-type barrier layer is provided directly under the p-type base layer to suppress the emission of the accumulated carriers proximal to the element surface.
However, the concentration of the n-type barrier layer cannot be increased because it is necessary to suppress breakdown between the n-type barrier layer and the p-type base layer. Thereby, a limitation occurs on the saturation voltage (Vce (sat)); and the characteristics of the semiconductor device unfortunately cannot be improved.